1. Field of the Invention
This invention relates to a resin coated metal plate and a worked article or product using the metal plate and also to a method for manufacturing same. More particularly, the invention relates to a resin coated metal plate wherein a metal plate, preferably a zinc-plated metal plate, is covered on the surface thereof with an epoxy resin-based matrix resin layer or an epoxy resin and polyester resin-based matrix resin layer, each containing conductive fillers, corrosion inhibitors and the like and which thus has excellent formability, weldability and corrosion resistance. The invention also relates to a method for manufacturing such worked articles.
The resin coated metal plate of a type, to which the invention is directed, is useful as a coated steel plate. Such a coated steel plate enables one to simplify a coating step when used, for example, as a coated steel plate such as of automotives, vehicles, vessels and also to permit application of processing grease to bent portions to be omitted, thereby enhancing productivity and providing products of high quality having excellent weldability and corrosion resistance.
2. Description of Related Art
For prior art techniques concerning the manufacture of coated metal plate-worked products, there is known, for example, a method disclosed, for example, in Japanese Laid-open Patent Application (JP-A) No. 6-23319. The present applicant has already developed and provided a technique set out in JP-A No. 2001-277422.
The invention of the JP-A No. 6-23319 discloses a coated metal plate using a paint which contains a polymer having polymerizable double bonds and crosslinkable hydroxyl groups and a blocked polyisocyanate compound. More particularly, when an active energy beam is irradiated to form a primarily cured film having good formability (flexibility), followed by a forming process. After the forming process, the film is baked to cause the blocked polyisocyanate to be reacted thereby providing a completely cured (secondarily cured) film imparted with high hardness and good stain resistance. If UV light is used as the active energy beam, it is recommended to use a photopolymerization initiator.
The invention set forth in the JP-A No. 2001-277422 makes use of a coating composition comprising two or more crosslinking resin components as a surface coating for steel plate. A steel surface is coated with this coating composition, and the resin coating layer is subsequently heated at low temperature, whereupon primary crosslinking reaction is allowed to proceed through a resin component capable of undergoing low-temperature crosslinking reaction while leaving unreacted reactive functional groups. The invention is characterized in that after completion of a metal forming process, heat of baking at the time of over coating is used for carrying out the secondary crosslinking reaction of a resin component that is crosslinkable at high temperature. According to this invention, features reside in that the overcoatability and silk printability are enhanced by means of the primarily crosslinked resin layer being hardened to an extent and the poor heat resistance attributed to the shortage in hardness of the primarily crosslinked resin layer is compensated through the secondary crosslinkage. In the invention, a low temperature-crosslinking epoxy resin is used as a low temperature reactive resin component and a melamine resin used as a high temperature-crosslinking resin composition. In addition, organic lubricants are added so as to improve formability.